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Hypothyroidism in Dogs

What is Hypothyroidism in Dogs?

Hypothyroidism in dogs is a prevalent endocrine disorder characterized by reduced production of thyroid hormones. The thyroid glands, situated on both sides of the neck near the throat, are responsible for generating these crucial hormones that regulate metabolism. When hormone production is insufficient, the dog’s bodily functions slow down.

Typically, hypothyroidism in dogs stems from inflammation or degeneration of the thyroid glands, with thyroid tumors being relatively rare. Middle-aged dogs, particularly those of medium-to-large breeds, are most commonly affected. Breeds such as Golden Retrievers, Dobermans, Dachshunds, Miniature Schnauzers, Cocker Spaniels, and Irish Setters are among those with a higher predisposition to the condition.


Symptoms of hypothyroidism in dogs manifest in various clinical signs:

  • Weight gain: Dogs with hypothyroidism often gain weight despite not showing an increased appetite. Pet parents may observe significant weight gain in their dogs despite moderate food intake.
  • Lethargy and reduced activity: Dogs affected by hypothyroidism may exhibit a preference for resting and sleeping rather than engaging in active play or exercise.
  • Heat-seeking behavior: Due to decreased thyroid hormone levels and subsequent lower metabolism, hypothyroid dogs may feel cold frequently. They may seek warmth by lying near sources of heat such as fireplaces or heat vents.
  • Chronic skin and ear infections: While allergies are common among dogs, recurring skin and ear infections could indicate an underlying issue like hypothyroidism.
  • Dry, brittle hair and thinning coat: Dogs with hypothyroidism may experience hair loss along their back or tail, leading to a thinning coat or a “rat tail” appearance.
  • Increased skin pigmentation: Some dogs with hypothyroidism may develop increased pigmentation of the skin.
  • Inability to regrow shaved hair: Dogs may struggle to regrow hair in areas where it has been shaved.

In addition to these common symptoms, some dogs may exhibit less typical signs of hypothyroidism such as reproductive problems, nervous system issues like nerve pain or hind leg weakness, small white fat deposits on the eyes, dry eye condition, or facial skin thickening resulting in drooping muscles.


The primary causes of hypothyroidism in dogs are inflammation of the thyroid gland (known as lymphocytic thyroiditis) and degeneration of the thyroid gland (referred to as idiopathic thyroid gland atrophy).

While the spontaneous occurrence of these conditions in some dogs lacks a definitive explanation, there is a recognized genetic predisposition. Additionally, a rare cause of hypothyroidism in dogs is cancer. However, this accounts for only a small percentage of hypothyroid patients.

The majority of hypothyroidism cases in dogs stem from either thyroid gland inflammation or degeneration, both of which can be effectively managed with medication.


Veterinarians employ several methods to diagnose hypothyroidism in dogs:

  • Physical Examination: The initial step involves a comprehensive physical examination of the dog, coupled with a detailed medical history. Pet owners should communicate any observed unusual behaviors or physical changes, providing a timeline of when these symptoms first appeared.
  • Bloodwork and Urinalysis: Basic bloodwork and a urinalysis are often conducted to assess the overall health of the dog. If skin changes are present, veterinarians may perform skin scrapes or smears to investigate possible secondary skin infections.
  • Blood Test for Diagnosis: Hypothyroidism is confirmed through a blood test. Veterinarians typically draw blood from the dog to conduct either in-clinic testing or send samples to an external laboratory for analysis.
  • Total Thyroxine Level Test: The primary diagnostic tool is a screening test called a total thyroxine level (Total T4 or TT4). This test measures the main thyroid hormone level in the dog. A low Total T4 level, combined with clinical signs of hypothyroidism, suggests a diagnosis.
  • Additional Blood Tests: In many cases, veterinarians proceed with additional blood tests, such as a free T4 level or a full thyroid panel, to confirm the diagnosis of hypothyroidism. Sometimes, dogs may exhibit a low Total T4 level without necessarily having hypothyroidism. Conversely, a dog could have a Total T4 level within the lower end of the normal range but still suffer from hypothyroidism. Confirmatory tests help in such scenarios, providing further clarity on the diagnosis.


The treatment for hypothyroidism in dogs involves administering an oral medication known as levothyroxine. This medication serves as a synthetic replacement for the thyroid hormone that the dog’s body lacks. It’s crucial to understand that while hypothyroidism can be managed with treatment, it cannot be cured.

Dogs diagnosed with hypothyroidism will require lifelong administration of the thyroid replacement hormone. The dosage of the medication is determined by the veterinarian based on the dog’s weight, as it comes in various strengths. Veterinarians typically schedule a follow-up appointment within a month to re-evaluate the dog’s condition through bloodwork and ensure that the dosage is appropriate.

Left untreated, hypothyroidism can significantly shorten a dog’s lifespan, as thyroid hormone impacts nearly every organ and aspect of metabolism. Dogs with untreated hypothyroidism may experience complications such as elevated cholesterol levels, weakened immune function, a decrease in heart rate, and neuromuscular symptoms, including unsteadiness, head tilting, and seizures. While treatment is effective in managing hypothyroidism, failure to address the condition can severely impact the dog’s quality of life.

Living and Management

Managing hypothyroidism in dogs involves lifelong therapy with oral thyroid hormone replacement. Over time, your dog’s tolerance to the medication may change, necessitating periodic dose adjustments. It’s advisable to have your dog’s blood thyroid levels checked every 6-12 months to ensure they are receiving the appropriate dosage of medication. Maintaining the correct thyroid hormone level is crucial for your dog’s long-term health.

Once your dog’s thyroid levels have normalized, you may observe weight loss as their overall condition improves, accompanied by increased energy levels. While it may take some time for your dog’s hair to fully regrow, gradual improvement in their skin and coat quality can be expected.

Hypothyroidism can lead to reduced tear production in dogs. Keep an eye on your dog’s eyes for any signs of green-yellow discharge, and consult your veterinarian if you notice any changes. Regular monitoring and communication with your veterinarian are essential for effectively managing your dog’s hypothyroidism and ensuring their ongoing well-being.

Hypothyroidism in Dogs FAQs

Is hypothyroidism curable?

Hypothyroidism is manageable but not curable. It is typically treated with lifelong oral synthetic thyroid hormone replacement medication (levothyroxine).

Can medication be overdosed?

Yes, thyroid medication can be overdosed, emphasizing the importance of ensuring your dog is on the correct dosage. Initially, your veterinarian will prescribe a standard dose based on your dog’s weight and will monitor their response through bloodwork. Metabolism and medication tolerance may change over time, necessitating periodic dose adjustments. Regular re-check appointments and thyroid level assessments every 6-12 months are recommended. Signs of medication overdose include excessive weight loss, irritability/hyperactivity, increased drinking and/or panting, and sleep disturbances.

How long do dogs live with hypothyroidism?

Dogs with hypothyroidism can lead normal, healthy lives with proper medication management. While the condition is not curable, it has an excellent prognosis, and patients generally respond well to treatment. Medically managed dogs have a normal life expectancy.

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